Exfoliated graphite-resin composite material and method for producing the same

ABSTRACT

There is provided an exfoliated graphite-resin composite material that has high dispersibility in resins and the like and is easily handled. An exfoliated graphite-resin composite material in which exfoliated graphite and a resin form a composite. When an amount of methylene blue adsorbed per g of the exfoliated graphite-resin composite material (μmol/g) is y, the amount of methylene blue adsorbed as measured based on a difference between an absorbance of a methanol solution of methylene blue at a concentration of 10 mg/L and an absorbance of a supernatant liquid obtained by introducing the exfoliated graphite-resin composite material into the methanol solution of methylene blue and performing centrifugation, and a BET specific surface area (m 2 /g) of the exfoliated graphite-resin composite material is x, a ratio y/x is 0.15 or more, and the BET specific surface area is 25 m 2 /g or more.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of patent applicationSer. No. 14/412,199, filed on Dec. 30, 2014, which is a 371 applicationof Application Serial No. PCT/JP2013/053470, filed on Feb. 14, 2013,which is based on Japanese Patent Application No. 2012-186463, filed onAug. 27, 2012, the entire contents of which are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to an exfoliated graphite-resin compositematerial obtained by exfoliating graphite or primary exfoliatedgraphite, and a method for producing the same.

BACKGROUND ART

Graphite is a stack in which a large number of graphenes are stacked. Byexfoliating graphite, graphene or exfoliated graphite having a smallernumber of stacked layers of graphene than graphite is obtained. Theexfoliated graphite is expected to be applied to electrically conductivematerials, thermally conductive materials, and the like.

In recent years, various methods of grafting a polymer on graphene orexfoliated graphite to increase the dispersibility of the graphene orexfoliated graphite in a resin, and the like have been studied. Forexample, the following Patent Literature 1 discloses a method forproducing graphene on which a polymer is grafted, by subjectingexfoliated graphene and a radical polymerizable monomer topolymerization in coexistent state.

CITATION LIST Patent Literature

Patent Literature 1: U.S. Pat. No. 7,659,350 B2

SUMMARY OF INVENTION Technical Problem

In the method in Patent Literature 1, graphite is previously exfoliated,and the thus obtained exfoliated graphene is used.

However, in conventionally known methods for exfoliating graphene, it isnecessary to treat raw material graphite with an acid, then heat theabove graphite to exfoliate the graphite, and further collect theobtained powder of graphene or exfoliated graphite. In this manner, inorder to obtain graphene or exfoliated graphite, it is necessary toexfoliate raw material graphite through a large number of complicatedsteps. In addition, in conventional methods, graphene or exfoliatedgraphite is obtained as a powder, and therefore, there is the problem ofdifficult handling.

It is a main object of the present invention to provide an exfoliatedgraphite-resin composite material that has high dispersibility in resinsand the like and is easily handled.

Solution to Problem

An exfoliated graphite-resin composite material according to the presentinvention is an exfoliated graphite-resin composite material in whichexfoliated graphite and a resin form a composite. In an exfoliatedgraphite-resin composite material according to a first invention in thisapplication, when the amount of methylene blue adsorbed (μmol/g)measured by the following method is y, and the BET specific surface area(m/g) is x, the ratio y/x is 0.15 or more, and the BET specific surfacearea is 25 m/g or more. The above amount of methylene blue adsorbed ismeasured based on the difference between the absorbance of a methanolsolution of methylene blue at a concentration of 10 mg/L and theabsorbance of a supernatant liquid obtained by introducing theexfoliated graphite-resin composite material into the methanol solutionof methylene blue, performing stirring, and then performingcentrifugation. This method for measuring the amount of methylene blueadsorbed will be described in detail in the subsequent description ofembodiments.

An exfoliated graphite-resin composite material according to a secondinvention in this application is an exfoliated graphite-resin compositematerial in which exfoliated graphite and a resin form a composite. Inthe exfoliated graphite-resin composite material, a pyrolysis initiationtemperature and pyrolysis end temperature of the resin in the compositematerial are higher than a pyrolysis initiation temperature andpyrolysis end temperature of the resin before the composite formation,respectively.

In another particular aspect of the exfoliated graphite-resin compositematerial according to the present invention, a content of the resin is1% by mass to 70% by mass.

In another particular aspect of the exfoliated graphite-resin compositematerial according to the present invention, the resin is a polymer of aradical polymerizable monomer.

A method for producing an exfoliated graphite-resin composite materialaccording to the present invention is a method for producing the aboveexfoliated graphite-resin composite material. In the method forproducing an exfoliated graphite-resin composite material according tothe present invention, a composition comprising graphite or primaryexfoliated graphite and a polymer, the polymer being fixed to thegraphite or primary exfoliated graphite, is provided. The polymercontained in the composition is pyrolyzed to exfoliate the graphite orprimary exfoliated graphite while leaving part of the polymer.

In a particular aspect of the method for producing an exfoliatedgraphite-resin composite material according to the present invention, inthe step of providing the composition, the polymer is grafted oradsorbed on the graphite or primary exfoliated graphite, and thus, thepolymer is fixed to the graphite or primary exfoliated graphite.

In the first embodiment of the method for producing an exfoliatedgraphite-resin composite material according to the present invention,the step of providing the composition comprises a step of providing amixture comprising the graphite or primary exfoliated graphite and aradical polymerizable monomer, and a step of polymerizing the radicalpolymerizable monomer contained in the mixture to form the polymer inwhich the radical polymerizable monomer is polymerized in the mixtureand graft the polymer on the graphite or primary exfoliated graphite.

In the second embodiment of the method for producing an exfoliatedgraphite-resin composite material according to the present invention, inthe step of providing the composition, the polymer is heated to atemperature in a temperature range of 50° C. or higher and 400° C. orlower in the presence of the graphite or primary exfoliated graphite tograft the polymer on the graphite or primary exfoliated graphite.

Various particular aspects of the method for producing an exfoliatedgraphite-resin composite material according to the present invention,including the above first embodiment or the above second embodiment,will be described below.

In a particular aspect of the method for producing an exfoliatedgraphite-resin composite material according to the present invention, inthe step of providing the composition, the composition further comprisesa pyrolyzable foaming agent. In this case, the graphite or primaryexfoliated graphite can be exfoliated much more effectively. Therefore,the specific surface area of the obtained exfoliated graphite can befurther increased.

In another particular aspect of the method for producing an exfoliatedgraphite-resin composite material according to the present invention,the pyrolyzable foaming agent is at least one heat foaming agentselected from the group consisting of compounds having structuresrepresented by the following formula (1) to formula (4).

In another particular aspect of the method for producing an exfoliatedgraphite-resin composite material according to the present invention, inthe step of pyrolyzing the polymer to exfoliate the graphite or primaryexfoliated graphite, the pyrolyzable foaming agent contained in themixture is pyrolyzed.

In still another particular aspect of the above first embodiment of themethod for producing an exfoliated graphite-resin composite materialaccording to the present invention, in the step of forming the polymerand grafting the polymer on the graphite or primary exfoliated graphite,the pyrolyzable foaming agent contained in the mixture is pyrolyzed.

In still another particular aspect of the above first embodiment of themethod for producing an exfoliated graphite-resin composite materialaccording to the present invention, the step of forming the polymer andgrafting the polymer on the graphite or primary exfoliated graphite isperformed by heating the mixture to polymerize the radical polymerizablemonomer contained in the mixture. In this case, both the polymerizationof the radical polymerizable monomer and the polymerization of thepolymer can be performed by simply heating the mixture. Therefore, thegraphite or primary exfoliated graphite can be exfoliated much moreeasily.

In still another particular aspect of the method for producing anexfoliated graphite-resin composite material according to the presentinvention, the radical polymerizable monomer is a vinyl-based monomer.Preferably, the vinyl-based monomer is a styrene monomer or glycidylmethacrylate. The styrene monomer is inexpensive, and therefore, theproduction cost of the exfoliated graphite-resin composite material canbe lowered. In the above-described first embodiment, as the radicalpolymerizable monomer, the styrene monomer can be preferably used. Inaddition, in the above-described second embodiment, as the abovepolymer, a polymer of glycidyl methacrylate is preferably used.

Advantageous Effects of Invention

In the exfoliated graphite-resin composite material according to thepresent invention, the distance between graphenes is increased, andtherefore, the specific surface area is large. In addition, theexfoliated graphite-resin composite material according to the presentinvention has a graphite structure in the central portion and has anexfoliated structure in which the distance between graphenes isincreased in the edge portion. Therefore, the exfoliated graphite-resincomposite material is more easily handled than conventional exfoliatedalloys. Further, the exfoliated graphite-resin composite materialaccording to the present invention comprises a resin and therefore hashigh dispersibility in other resins.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing the TG/DATA measurement results ofpolystyrene in Example 1.

FIG. 2 is a diagram showing the TG/DATA measurement results of polyvinylacetate in Example 2.

FIG. 3 is a diagram showing the TG/DATA measurement results ofpolypropylene glycol in Example 3.

FIG. 4 is a diagram showing the TG/DATA measurement results of anexfoliated graphite-resin composite material obtained in Example 1.

FIG. 5 is a diagram showing the TG/DATA measurement results of anexfoliated graphite-resin composite material obtained in Example 2.

FIG. 6 is a diagram showing the TG/DATA measurement results of anexfoliated graphite-resin composite material obtained in Example 3.

FIG. 7 is a diagram showing the XRD spectrum of the exfoliatedgraphite-resin composite material obtained in Example 1.

FIG. 8 is a diagram showing the XRD spectrum of the exfoliatedgraphite-resin composite material obtained in Example 2.

FIG. 9 is a diagram showing the XRD spectrum of the exfoliatedgraphite-resin composite material obtained in Example 3.

FIG. 10 is a photograph of the exfoliated graphite obtained by Example 1taken by a scanning electron microscope (SEM).

FIG. 11 is a photograph of the exfoliated graphite obtained by Example 2taken by the scanning electron microscope (SEM).

FIG. 12 is a photograph of the exfoliated graphite obtained by Example 3taken by the scanning electron microscope (SEM).

FIG. 13 is a diagram showing the TG/DATA measurement results of anexfoliated graphite-resin composite material obtained in ReferenceExample 1.

FIG. 14 is a diagram showing the TG/DATA measurement results of anexfoliated graphite-resin composite material obtained in ReferenceExample 2.

FIG. 15 is a diagram showing the TG/DATA measurement results of anexfoliated graphite-resin composite material obtained in ReferenceExample 3.

FIG. 16 is a diagram showing the relationship between the BET specificsurface area (m²/g) and the amount of methylene blue adsorbed (μmol/g)in exfoliated graphite-resin composite materials obtained in Examples 4to 14 and Reference Examples 4 to 7 and known carbonaceous materials.

FIG. 17 is an enlarged diagram showing the range surrounded by thedotted line in FIG. 16.

DESCRIPTION OF EMBODIMENTS

An exfoliated graphite-resin composite material and a method forproducing the same according to the present invention will be describedin detail below.

[Exfoliated Graphite-Resin Composite Material]

The exfoliated graphite-resin composite material according to thepresent invention is a material in which exfoliated graphite and a resinform a composite.

The exfoliated graphite-resin composite material comprises exfoliatedgraphite and a resin.

The exfoliated graphite contained in the exfoliated graphite-resincomposite material is one in which at least a part of graphene layers ofgraphite or primary exfoliated graphite that is a raw material isexfoliated. Graphite is a stack of a plurality of graphene layers andis, for example, natural graphite, synthetic graphite, or expandedgraphite. As the graphite used as a raw material, expanded graphite ispreferred. The distance between graphene layers is larger in expandedgraphite than in usual graphite, and therefore, the expanded graphitecan be easily exfoliated. Therefore, by using expanded graphite as thegraphite, the exfoliated graphite-resin composite material can be easilyproduced.

In the above graphite, the number of stacked layers of graphene is about100000 or more to 1000000, and the BET specific surface area is a valueof 22 m²/g or less. In addition, the exfoliated graphite-resin compositematerial of the present invention refers to one in which the number ofstacked layers of graphene is 3000 or less.

In an exfoliated graphite-resin composite material according to a firstinvention in this application, when the amount of methylene blueadsorbed (μmol/g) is y, and the BET specific surface area (m²/g) is x,the ratio y/x is 0.15 or more, more preferably 0.27 or more, and morepreferably 0.39 or more.

The above amount of methylene blue adsorbed is obtained by the followingmethod. The exfoliated graphite-resin composite material is introducedinto a methanol solution of methylene blue at a concentration of 10mg/L, and the mixture is stirred. Next, the mixture is centrifuged, anda change in the absorbance of the obtained supernatant liquid at themaximum absorption wavelength is observed. The methylene blue isadsorbed by conjugation on the portions of the exfoliated graphite-resincomposite material where graphene is stacked. On the other hand, themethylene blue emits fluorescence by irradiation with light. When themethylene blue is adsorbed on the graphene, it does not emitfluorescence. In other words, the fluorescence intensity decreases.Therefore, the amount of methylene blue adsorbed can be obtained fromthe amount of decrease in fluorescence intensity obtained from the abovesupernatant liquid with respect to the fluorescence intensity of theoriginal methylene blue.

On the other hand, there is a correlation between the above amount ofmethylene blue adsorbed and the specific surface area of a carbonaceousmaterial. In conventionally known spherical graphite particles, when thespecific surface area (m²/g) obtained by BET is x, and the above amountof methylene blue adsorbed (μmol/g) is y, the relationship y≈0.13xholds. This indicates that the larger the specific surface area is, thelarger the amount of methylene blue adsorbed is. Therefore, the amountof methylene blue adsorbed can be an indicator replacing the specificsurface area.

In the exfoliated graphite-resin composite material according to thefirst present invention, the ratio y/x is 0.15 or more as describedabove. In the conventional spherical graphite particles, y≈0.13x. On theother hand, in the present invention, y/x is 0.15 or more, andtherefore, the exfoliated graphite-resin composite material according tothe first present invention is distinguished from the conventionalspherical graphite particles. In other words, the amount of methyleneblue adsorbed is larger in the exfoliated graphite-resin compositematerial according to the present invention than in the conventionallyknown spherical graphite though the BET specific surface area is thesame. This is considered to be because in the exfoliated graphite-resincomposite material according to the present invention, condensationoccurs to some extent in a dry state, but the distance between graphenesis increased in a wet state such as in methanol compared with in the drystate.

In a second invention in this application, the pyrolysis initiationtemperature and pyrolysis end temperature of a resin in an exfoliatedgraphite-resin composite material are higher than the pyrolysisinitiation temperature and pyrolysis end temperature of the resin beforecomposite formation, respectively. In the present invention, thepyrolysis initiation temperature and pyrolysis end temperature refer toTAG measurement-dependent decomposition initiation temperature anddecomposition end point temperature, respectively.

In the exfoliated graphite-resin composite materials according to thefirst and second inventions in this application, not only is thedistance between graphenes increased, but the resin forms a compositewith the exfoliated graphite. Therefore, the exfoliated graphite-resincomposite materials have excellent dispersibility when added to a resinmaterial. Further, when added to a resin, the exfoliated graphite-resincomposite material is desirably added in a state of a dispersion inwhich the exfoliated graphite-resin composite material is dispersed inan organic solvent. In the dispersion, the distance between graphenes isincreased, and aggregation can be suppressed. Therefore, even if theamount of the exfoliated graphite-resin composite material added isdecreased, the exfoliated graphite-resin composite material can bedispersed much more uniformly in the resin. In addition, the exfoliatedgraphite-resin composite material is less likely to precipitate in adispersion or solution, and therefore, the pot life, that is, usabletime, of the dispersion or solution can also be increased. Therefore,preferably, the exfoliated graphite-resin composite material accordingto the present invention is desirably prepared as a dispersion orsolution in which the exfoliated graphite-resin composite material isdispersed or dissolved in an organic solvent.

The BET specific surface area of the exfoliated graphite-resin compositematerial is 25 m²/g or more, preferably 35 m²/g or more, more preferably45 m²/g or more, and more preferably 100 m²/g or more. The upper limitvalue of the BET specific surface area of the exfoliated graphite-resincomposite material is usually 2500 m²/g or less.

The exfoliated graphite may be one using primary exfoliated graphite asa raw material instead of graphite. The primary exfoliated graphitewidely includes, in addition to exfoliated graphite obtained byexfoliating graphite, and the exfoliated graphite-resin compositematerial of the present invention, exfoliated graphite obtained byexfoliating graphite by various methods described later. The primaryexfoliated graphite is obtained by exfoliating graphite, and therefore,its specific surface area is larger than that of graphite.

The resin contained in the exfoliated graphite-resin composite materialis preferably a polymer of a radical polymerizable monomer. The resinmay be a copolymer of a plurality of types of radical polymerizablemonomers or a homopolymer of one type of radical polymerizable monomer.The radical polymerizable monomer is not particularly limited as long asit is a monomer having a radical polymerizable functional group.Examples of the radical polymerizable monomer include styrene, methylα-ethylacrylate, methyl α-benzylacrylate, methylα-[2,2-bis(carbomethoxy)ethyl]acrylate, dibutyl itaconate, dimethylitaconate, dicyclohexyl itaconate, α-methylene-δ-valerolactone,α-methylstyrene, α-substituted acrylates comprising α-acetoxystyrene,vinyl monomers having a glycidyl group or a hydroxyl group such asglycidyl methacrylate, 3,4-epoxycyclohexylmethyl methacrylate,hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropylacrylate, and 4-hydroxybutyl methacrylate; vinyl monomers having anamino group such as allylamine, diethylaminoethyl (meth)acrylate, anddimethylaminoethyl (meth)acrylate; monomers having a carboxyl group suchas methacrylic acid, maleic anhydride, maleic acid, itaconic acid,acrylic acid, crotonic acid, 2-acryloyloxyethyl succinate,2-methacryloyloxyethyl succinate, and 2-methacryloyloxyethylphthalicacid; monomers having a phosphate group such as Phosmer M, Phosmer CL,Phosmer PE, Phosmer MH, and Phosmer PP manufactured by Uni-Chemical Co.,Ltd.; monomers having an alkoxysilyl group such as vinyltrimethoxysilaneand 3-methacryloxypropyltrimethoxysilane; and (meth)acrylate-basedmonomers having an alkyl group, a benzyl group, or the like. Preferredexamples of the radical polymerizable monomer include vinyl-basedmonomers. Particular examples include an inexpensive styrene monomer.

The content of the resin in the exfoliated graphite-resin compositematerial is preferably 1% by mass to 70% by mass. Thus, by the compositeformation of the resin, it is possible to increase dispersibility in amatrix resin or the like much more and increase the distance betweengraphenes in the edge portion more reliably. The content is morepreferably 5% by mass to 30% by mass, further preferably 10% by mass to20% by mass.

The exfoliated graphite-resin composite material of the presentinvention is characterized by being relatively less likely to fly. Thisis considered to be because a polymer obtained by polymerizing the aboveradical polymerizable monomer is not completely decomposed and is leftin a pyrolysis step as described later. In other words, it is consideredthat the polymer positioned in portions sandwiched between the graphenelayers in the exfoliated graphite is sandwiched between the graphenes onboth sides and therefore is not completely pyrolyzed around thepyrolysis temperature. Therefore, the exfoliated graphite-resincomposite material of the present invention is easily handled.

In addition, in the exfoliated graphite-resin composite materialaccording to the present invention, the interlayer distance betweengraphenes is increased, and the specific surface area is large. Further,the exfoliated graphite-resin composite material according to thepresent invention has a graphite structure in the central portion andhas an exfoliated structure in the edge portion. Therefore, theexfoliated graphite-resin composite material is more easily handled thanconventional exfoliated alloys. In addition, the exfoliatedgraphite-resin composite material according to the present inventioncomprises a resin and therefore has high dispersibility in other resins.Particularly, when other resins are resins having a high affinity forthe resin contained in the exfoliated graphite-resin composite material,the dispersibility of the exfoliated graphite-resin composite materialin the other resins is higher.

Such an exfoliated graphite-resin composite material can be produced,for example, by a production method as described below.

[Method for Producing Exfoliated Graphite-Resin Composite Material]

(Step of Providing Raw Material Composition)

In a method for producing an exfoliated graphite-resin compositematerial according to the present invention, a composition comprisingthe above graphite or primary exfoliated graphite and the above polymer,the polymer being fixed to the graphite or primary exfoliated graphite,is provided first. As the step of providing this composition, forexample, the following first and second methods in which the polymer isgrafted on the graphite or primary exfoliated graphite to fix thepolymer to the graphite or primary exfoliated graphite, and a thirdmethod in which the polymer is adsorbed on the graphite or primaryexfoliated graphite to fix the polymer to the graphite or primaryexfoliated graphite can be used.

(First Method)

In the first method, first, a mixture comprising the above graphite orprimary exfoliated graphite and the above radical polymerizable monomeris provided as a raw material. Next, the radical polymerizable monomercontained in the mixture is polymerized to form a polymer in which theabove radical polymerizable monomer is polymerized in the mixture andgraft the polymer on the graphite or primary exfoliated graphite.

In the first method, first, a composition comprising the graphite orprimary exfoliated graphite and the radical polymerizable monomer isprovided.

The blending ratio between the graphite and the radical polymerizablemonomer is not particularly limited and is desirably a proportion of 1:1to 1:100 in terms of a mass ratio. By setting the blending ratio in arange, it is possible to exfoliate the graphite or primary exfoliatedgraphite effectively to obtain the exfoliated graphite-resin compositematerial much more effectively.

In the step of providing the above composition, preferably, acomposition further comprising a pyrolyzable foaming agent thatgenerates a gas in pyrolysis is provided. In this case, the graphite orprimary exfoliated graphite can be exfoliated much more effectively byheating described later.

The above pyrolyzable foaming agent is not particularly limited as longas it is a compound that decomposes spontaneously by heating andgenerates a gas during the decomposition. As the above pyrolyzablefoaming agent, for example, azocarboxylic acid-based,diazoacetamide-based, azonitrile compound-based,benzenesulfohydrazine-based, or nitroso compound-based foaming agents orthe like that generate a nitrogen gas during decomposition, or foamingagents that generate carbon monoxide, carbon dioxide, methane, aldehyde,or the like during decomposition can be used. The above pyrolyzablefoaming agent may be used alone, or a plurality of types of foamingagents may be used in combination.

Preferably, as the above pyrolyzable foaming agent, azodicarbonamide(ADCA) having a structure represented by the following formula (1) andfoaming agents having structures represented by the following formulas(2) to (4) can be used. These foaming agents decompose spontaneously byheating and generate a nitrogen gas during the decomposition.

The pyrolysis temperature of the above pyrolyzable foaming agent is notparticularly limited and may be lower or higher than a temperature atwhich the above radical polymerizable monomer spontaneously initiatespolymerization. For example, the pyrolysis temperature of the ADCAhaving the structure represented by the above formula (1) is 210° C.,which is a temperature higher than a temperature at which styrenespontaneously initiates polymerization, 150° C., when the above radicalpolymerizable monomer is styrene. The pyrolysis initiation temperaturesof pyrolyzable foaming agents having the structures represented by theabove formulas (2) to (4) are 88° C., 96° C., and 110° C. in order, andthese are temperatures lower than the temperature at which styrenespontaneously initiates polymerization, 150° C.

The blending ratio between the above graphite or primary exfoliatedgraphite and the above pyrolyzable foaming agent is not particularlylimited, and 100 parts by weight to 300 parts by weight of the abovepyrolyzable foaming agent is preferably blended based on 100 parts byweight of the above graphite or primary exfoliated graphite. By settingthe amount of the above pyrolyzable foaming agent blended in the aboverange, it is possible to exfoliate the above graphite or primaryexfoliated graphite much more effectively to obtain the exfoliatedgraphite-resin composite material effectively.

The method for providing the above composition is not particularlylimited. Examples of the method include a method of dispersing the abovegraphite or primary exfoliated graphite in the above radicalpolymerizable monomer using the above radical polymerizable monomer as adispersion medium. In addition, the above composition further comprisingthe above pyrolyzable foaming agent can be provided by dissolving ordispersing the above pyrolyzable foaming agent in the above radicalpolymerizable monomer.

Next, the step of polymerizing the above radical polymerizable monomercontained in the above composition to form a polymer in which the aboveradical polymerizable monomer is polymerized in the above composition isperformed.

At this time, the above radical polymerizable monomer forms a freeradical, and thus, the above radical polymerizable monomer undergoesradical polymerization, and thus, the polymer in which the above radicalpolymerizable monomer is polymerized is formed. On the other hand, thegraphite contained in the above composition is a stack of a plurality ofgraphene layers and therefore has radical trapping properties.Therefore, when the above radical polymerizable monomer is subjected topolymerization in the above composition comprising the above graphite orprimary exfoliated graphite, the above free radical is adsorbed on theends and surfaces of the graphene layers of the above graphite orprimary exfoliated graphite. Therefore, the above polymer or the aboveradical polymerizable monomer having the above free radical formedduring the polymerization is grafted on the ends and surfaces of thegraphene layers of the above graphite or primary exfoliated graphite.

Examples of the method for polymerizing the above radical polymerizablemonomer contained in the above composition include a method of heatingthe above composition to the temperature at which the above radicalpolymerizable monomer spontaneously initiates polymerization or higher.By heating the above composition to the above temperature or higher, afree radical can be formed in the above radical polymerizable monomercontained in the above composition. Thus, the above-describedpolymerization and grafting can be performed.

When the above radical polymerizable monomer is polymerized by heatingas described above, both the polymerization of the above radicalpolymerizable monomer and the pyrolysis of the above polymer describedlater can be performed by simply heating the above composition.Therefore, the exfoliation of the graphite or primary exfoliatedgraphite is much easier.

The above heating method is not particularly limited as long as it is amethod that can heat the above composition to the above temperature orhigher. The above composition can be heated by an appropriate method andapparatus. In addition, in the above heating, heating may be performedwithout sealing, that is, under normal pressure.

In addition, in order to reliably polymerize the above radicalpolymerizable monomer, after the above composition is heated to atemperature equal to or higher than the temperature at which the aboveradical polymerizable monomer spontaneously initiates polymerization,the above temperature may be further maintained for a certain time. Thetime that the above composition is maintained around the abovetemperature is preferably in the range of 0.5 to 5 hours thoughdepending on the type and amount of the radical polymerizable monomerused.

After the step of forming the above polymer, the step of heating theabove composition to the pyrolysis temperature of the above polymer topyrolyze the above polymer while leaving part of the polymer isperformed. Thus, the above polymer contained in the above composition,the above polymer grafted on the ends and surfaces of the graphenelayers of the above graphite or primary exfoliated graphite, and thelike are pyrolyzed. In the present invention, the pyrolysis temperatureof the above polymer refers to TAG measurement-dependent decompositionend point temperature. For example, when the polymer is polystyrene, thepyrolysis temperature of the above polymer is about 350° C.

At this time, when the above polymer grafted on the ends and surfaces ofthe graphene layers of the above graphite or primary exfoliatedgraphite, and the like are pyrolyzed, exfoliation force occurs betweenthe above graphene layers. Therefore, by pyrolyzing the above polymerand the like, the above graphite or primary exfoliated graphite can beexfoliated between the graphene layers of the above graphite or primaryexfoliated graphite to obtain exfoliated graphite.

In addition, part of the polymer is left in the composition even by thispyrolysis. The pyrolysis initiation temperature and pyrolysis endtemperature of the resin in the exfoliated graphite-resin compositematerial obtained by the pyrolysis are higher than the pyrolysisinitiation temperature and pyrolysis end temperature of the resin beforethe composite formation, respectively.

In the present invention, the exfoliated graphite is a graphene stackafter exfoliation obtained by subjecting the original graphite orprimary exfoliated graphite to exfoliation treatment, and refers to agraphene stack having a larger specific surface area than the aboveoriginal graphite or primary exfoliated graphite, or a graphene stack inwhich the decomposition end point of the original graphite or primaryexfoliated graphite shifts to lower temperature.

The above heating method is not particularly limited as long as it is amethod that can heat the above composition to the pyrolysis temperatureof the above polymer. The above composition can be heated by anappropriate method and apparatus. In addition, in the above heating,heating may be performed without sealing, that is, under normalpressure. Therefore, exfoliated graphite can be produced inexpensivelyand easily.

Pyrolysis such that the resin is left can be achieved by adjusting theheating time. In other words, by shortening the heating time, the amountof the resin left can be increased. In addition, by lowering the heatingtemperature, the amount of the resin left can also be increased.

Also in the second method and the third method described later, in thestep of heating the above composition so as to leave part of thepolymer, the heating temperature and the heating time may be adjusted.

After the above composition is heated to a temperature equal to orhigher than the pyrolysis temperature of the above polymer, the abovetemperature may be further maintained for a certain time, when the abovepolymer can be pyrolyzed so that part of the polymer is left, while partof the polymer is left in the composition. The time that the abovecomposition is maintained around the above temperature is preferably inthe range of 0.5 to 5 hours though depending on the type and amount ofthe radical polymerizable monomer used.

In addition, when the above radical polymerizable monomer is polymerizedby heating in the step of forming the above polymer, heat treatment inthe step of forming the above polymer, and heat treatment in the step ofpyrolyzing the above polymer described later may be continuouslyperformed by the same method and apparatus.

In the above heating, in a case where the above composition furthercomprises a pyrolyzable foaming agent, when the above composition isheated to the pyrolysis temperature of the above pyrolyzable foamingagent, the above pyrolyzable foaming agent is pyrolyzed in the abovecomposition. On the other hand, the above pyrolyzable foaming agentgenerates a gas and foams during pyrolysis. At this time, when the abovepyrolyzable foaming agent is pyrolyzed between the graphene layers ofthe above graphite or primary exfoliated graphite, the above gasgenerated by the above pyrolysis enters between the above graphenelayers, and the space between the above graphene layers is increased.Thus, exfoliation force occurs between the above graphene layers, andtherefore, the above graphite or primary exfoliated graphite can befurther exfoliated. Therefore, by using the above pyrolyzable foamingagent, the specific surface area of the obtained exfoliated graphite canbe increased much more.

In the present invention, by using the above radical polymerizablemonomer and/or the above polymer and the above pyrolyzable foaming agentin combination, the graphite or primary exfoliated graphite can beexfoliated much more effectively. The reason why the graphite or primaryexfoliated graphite can be exfoliated much more effectively by such amethod is not certain, but the following reason is considered. Asdescribed above, when the above radical polymerizable monomer forms afree radical, the above polymer or the above radical polymerizablemonomer having the above free radical formed during the polymerizationis grafted on the ends and surfaces of the graphene layers of the abovegraphite or primary exfoliated graphite. Therefore, the above freeradical is trapped in the graphene layers of the above graphite orprimary exfoliated graphite. On the other hand, the above pyrolyzablefoaming agent has the property of high affinity for radicals andtherefore is attracted to the free radical trapped in the graphenelayers of the above graphite or primary exfoliated graphite in the abovecomposition. Therefore, the above pyrolyzable foaming agent is easilypyrolyzed around the stacked surfaces of the graphene sheets of thegraphite or primary exfoliated graphite. Therefore, exfoliation forcecan be effectively applied between the graphene layers of the abovegraphite or primary exfoliated graphite by the pyrolysis of the abovepyrolyzable foaming agent.

The pyrolysis of the above pyrolyzable foaming agent need notnecessarily be performed in the step of pyrolyzing the above polymer.For example, when the pyrolysis temperature of the above pyrolyzablefoaming agent is lower than the temperature at which the above radicalpolymerizable monomer spontaneously initiates polymerization, the abovepyrolyzable foaming agent may be pyrolyzed when the above radicalpolymerizable monomer is polymerized by heating in the step of formingthe above polymer. In addition, the pyrolysis of the above pyrolyzablefoaming agent may be before the polymerization of the radicalpolymerizable monomer, after the polymerization, or simultaneous withthe polymerization.

In addition, in order to reliably pyrolyze the above pyrolyzable foamingagent, after the above composition is heated to a temperature equal toor higher than the pyrolysis temperature of the above pyrolyzablefoaming agent, the above temperature may be further maintained for acertain time. The time that the above composition is maintained aroundthe above temperature is preferably in the range of 0.5 to 5 hoursthough depending on the type and amount of the pyrolyzable foaming agentused.

(Second Method)

In the second method, in the step of providing a composition comprisinggraphite or primary exfoliated graphite and a polymer in which a radicalpolymerizable monomer is polymerized, the polymer being grafted on thegraphite or primary exfoliated graphite, the polymer is heated to atemperature in the temperature range of 50° C. or higher and 400° C. orlower in the presence of the graphite or primary exfoliated graphite tograft the polymer on the graphite or primary exfoliated graphite. Inother words, in the first method, a radical polymerizable monomer ispolymerized in the presence of graphite or primary exfoliated graphiteto form a polymer and promote the grafting of the polymer on thegraphite or primary exfoliated graphite, whereas in the second method,by heating a previously obtained polymer to the above particulartemperature range in the presence of graphite or primary exfoliatedgraphite, a polymer radical formed by pyrolyzing the polymer can bedirectly grafted on the graphite or primary exfoliated graphite.

As the polymer in the second method, an appropriate pyrolyticallyradical-forming polymer can be used.

Most organic polymers generate radicals at decomposition temperature.Therefore, as polymers that form radicals around the above decompositiontemperature, many organic polymers can be used. However, preferably,polymers of radical polymerizable monomers such as vinyl-based monomersare preferably used. Examples of such vinyl-based monomers, that is,vinyl group-containing monomers, include monomers such as ethylacrylate, butyl acrylate, 2-ethylhexyl acrylate, and benzyl acrylate.Preferred examples include styrene and glycidyl methacrylate. Inaddition, examples of polymers obtained by polymerizing the above vinylgroup-containing monomers can include alkyl (meth)acrylate esters,polypropylene, polyvinyl phenol, polyphenylene sulfide, andpolyphenylene ether.

In addition, polymers containing halogen elements such as chlorine, suchas polyvinyl chloride, chlorinated vinyl chloride resins, ethylenefluoride resins, vinylidene fluoride resins, and vinylidene chlorideresins, and the like can also be used. Ethylene vinyl acetate copolymers(EVA), polyvinyl acetal, polyvinylpyrrolidone, and copolymers thereofcan also be used. Polymers obtained by cationic polymerization such aspolyisobutylene and polyalkylene ethers can also be used.

Polyurethanes, epoxy resins, modified silicone resins, silicone resins,and the like obtained by crosslinking oligomers can also be used.

Polyallylamine may be used, and in this case, an amino group can begrafted on the graphite or primary exfoliated graphite. Polyvinyl phenoland polyphenols may be used, and in this case, phenolic OH can begrafted on the graphite or primary exfoliated graphite. In addition,when a polymer having a phosphate group is used, the phosphate group canbe grafted.

In addition, condensation polymers such as polyesters and polyamides maybe used. In this case, the concentration of radicals obtained atdecomposition temperature is low, but decomposition products aregrafted.

As the above previously provided polymer, homopolymers of glycidylmethacrylate, polystyrene, polyvinyl acetate, polypropylene glycol,polybutyral, and the like are preferably used. By using these polymers,the graphite or primary exfoliated graphite can be exfoliated much moreeffectively.

In the second method, the blending ratio between the above graphite orprimary exfoliated graphite and the above polymer is not particularlylimited and is desirably a proportion of 1:5 to 1:20 in terms of aweight ratio. By setting the blending ratio in this range, it ispossible to exfoliate the graphite or primary exfoliated graphite moreeffectively to obtain the exfoliated graphite-resin composite materialeffectively.

Also in the second method, as in the case of the first method, in thestep of providing the composition, preferably, it is desired to furthercontain a pyrolyzable foaming agent in the composition. As in the caseof the first method, the graphite or primary exfoliated graphite can beexfoliated much more effectively by heating that causes the pyrolysis ofthe polymer described later.

The pyrolyzable foaming agents that can be used are similar to those inthe case of the first method. Therefore, preferably, it is desired touse the foaming agents having the structures represented by formula (1)to (4) described above.

Also in the second method, the blending ratio between the graphite orprimary exfoliated graphite and the pyrolyzable foaming agent is notparticularly limited, and the pyrolyzable foaming agent is preferablyblended in the proportion of 100 to 300 parts by weight based on 100parts by weight of the graphite or primary exfoliated graphite. When theblending ratio is in this range, the graphite or primary exfoliatedgraphite can be exfoliated much more effectively.

Also in the second method, the specific method for providing thecomposition is not limited. Examples of the specific method include amethod of introducing the above polymer and graphite or primaryexfoliated graphite into an appropriate solvent or dispersion medium andheating the mixture.

The polymer is grafted on the graphite or primary exfoliated graphite bythe above heating. This heating temperature is desirably in the range of50° C. or higher and 400° C. or lower. By setting the heatingtemperature in this temperature range, the polymer can be effectivelygrafted on the graphite. Thus, the graphite or primary exfoliatedgraphite can be exfoliated much more effectively. The reason for this isconsidered as follows.

By heating the polymer obtained by polymerizing the above radicalpolymerizable monomer, part of the polymer decomposes, and a radical istrapped in the graphene layers of the graphite or primary exfoliatedgraphite. Therefore, the polymer is grafted on the graphite or primaryexfoliated graphite. Then, when the polymer is decomposed and fired in aheating step described later, large stress is applied to the graftingsurface of the polymer where the polymer is grafted on the graphite orprimary exfoliated graphite. Therefore, it is considered thatexfoliation force acts starting from the grafting point, and thedistance between the graphene layers is effectively increased.

(Third Method)

Examples of the third method can include a method of dissolving ordispersing the above graphite and the above polymer in an appropriatesolvent. As such a solvent, tetrahydrofuran, methyl ethyl ketone,toluene, ethyl acetate, and the like can be used.

In addition, when the pyrolyzable foaming agent is used, the pyrolyzablefoaming agent may be further added and dispersed or dissolved in theabove solvent.

In addition, in the third method, as the above composition, acomposition in which a polymer is adsorbed on graphite or primaryexfoliated graphite is provided in a solvent. The method for adsorbingthe polymer on the graphite or primary exfoliated graphite is notparticularly limited. The polymer has adsorption properties on graphite,and therefore, a method of mixing the graphite or primary exfoliatedgraphite with the polymer in the above-described solvent can be used.Preferably, in order to adsorb the polymer on the graphite or primaryexfoliated graphite more effectively, ultrasonic treatment is desirablycarried out. The ultrasonic treatment method is not particularlylimited. For example, a method of irradiation with ultrasonic waves atabout 100 W and an oscillation frequency of about 28 kHz using anappropriate ultrasonic treatment apparatus can be used.

In addition, the ultrasonic treatment time is also not particularlylimited and may be equal to or more than the time required for thepolymer to be adsorbed on the graphite. For example, in order to adsorbpolyvinyl acetate on the graphite, the ultrasonic treatment may bepreferably maintained for about 30 minutes or 60 minutes, morepreferably about 120 minutes.

It is considered that the adsorption of the polymer is due to theinteraction of the surface energy of the graphite with the polymer.

(Step of Exfoliating Graphite by Pyrolysis of Polymer)

In all of the above first method, second method, and third method, afterthe composition is provided as described above, the polymer contained inthe composition is pyrolyzed. Thus, the graphite or primary exfoliatedgraphite is exfoliated while part of the polymer is left, and theexfoliated graphite-resin composite material can be obtained. In orderto perform the pyrolysis of the polymer in this case, the abovecomposition may be heated to the pyrolysis temperature of the polymer orhigher. More specifically, the above composition is heated to thepyrolysis temperature of the polymer or higher, and the polymer isfurther fired. At this time, the polymer is fired to the extent that thepolymer is left in the composition. Thus, the exfoliated graphite-resincomposite material can be obtained. For example, the pyrolysistemperature of polystyrene is about 380° C. to 450° C., the pyrolysistemperature of polyglycidyl methacrylate is about 400° C. to 500° C.,and the pyrolysis temperature of polybutyral is about 550° C. to 600° C.in the air.

It is considered that the exfoliated graphite-resin composite materialcan be obtained by the pyrolysis of the above polymer for theabove-described reason, that is, because when the polymer grafted on thegraphite is fired, large stress acts on the grafting point, and thus,the distance between the graphenes increases.

In the first method, it has been described that the heating forpolymerizing the radical polymerizable monomer and the pyrolysis of theabove polymer may be continuously carried out in the same heating step.Also in the second method, the heating step for grafting the abovepolymer on the graphite or primary exfoliated graphite and the heatingstep of pyrolyzing the above polymer may be continuously carried out.

Further, it is desired to carry out both the first method and the secondmethod a plurality of times. For example, it is possible to provide acomposition by the first method, then pyrolyze the polymer to obtainexfoliated graphite in which substantially no polymer is contained, andthen further repeat the first method one or more times using theobtained exfoliated graphite as primary exfoliated graphite that is araw material in the first method, to obtain an exfoliated graphite-resincomposite material having a much larger specific surface area.Similarly, it is possible to provide a composition by the second method,then pyrolyze the polymer to obtain exfoliated graphite in whichsubstantially no polymer is contained, and then further carry out thesecond method and the pyrolysis of the polymer using the obtainedexfoliated graphite as primary exfoliated graphite that is a rawmaterial in the second method, to obtain an exfoliated graphite-resincomposite material. Also in these cases, an exfoliated graphite-resincomposite material having a much larger specific surface area can beobtained. For example, it is possible to provide a composition by thefirst method, then pyrolyze the polymer to obtain an exfoliatedgraphite-resin composite material, and then further repeat the firstmethod one or more times using the obtained exfoliated graphite-resincomposite material as primary exfoliated graphite that is a raw materialin the first method, to obtain an exfoliated graphite-resin compositematerial having a much larger specific surface area. Similarly, it ispossible to provide a composition by the second method, then pyrolyzethe polymer to obtain an exfoliated graphite-resin composite material,and then further carry out the second method and the pyrolysis of thepolymer using the obtained exfoliated graphite-resin composite materialas primary exfoliated graphite that is a raw material in the secondmethod, to obtain an exfoliated graphite-resin composite material.

Further, it is possible to heat a composition provided by the firstmethod to obtain exfoliated graphite in which substantially no polymeris contained, and then, using the exfoliated graphite as primaryexfoliated graphite as a raw material in the second method, subsequentlyobtain exfoliated graphite as in the second method. On the contrary, itis possible to heat a composition obtained by the second method toobtain exfoliated graphite in which substantially no polymer iscontained, then subsequently provide a composition as in the firstmethod using the exfoliated graphite as primary exfoliated graphite thatis a raw material in the first method, and further pyrolyze the polymerby heating, to obtain exfoliated graphite. By repeating exfoliation bythe production method of the present invention one or more times furtherusing the above exfoliated graphite in which substantially no polymer iscontained obtained by pyrolysis, as primary exfoliated graphite as a rawmaterial, in this manner, an exfoliated graphite-resin compositematerial having a much larger specific surface area can be obtained.

It is possible to heat a composition provided by the first method toobtain an exfoliated graphite-resin composite material, and then, usingthe exfoliated graphite-resin composite material as primary exfoliatedgraphite as a raw material in the second method, subsequently obtain anexfoliated graphite-resin composite material as in the second method. Onthe contrary, it is possible to heat a composition obtained by thesecond method to obtain an exfoliated graphite-resin composite material,then subsequently provide a composition as in the first method using theexfoliated graphite-resin composite material as primary exfoliatedgraphite that is a raw material in the first method, and furtherpyrolyze the polymer by heating, to obtain an exfoliated graphite-resincomposite material. By repeating exfoliation by the production method ofthe present invention one or more times further using an exfoliatedgraphite-resin composite material as primary exfoliated graphite as araw material in this manner, an exfoliated graphite-resin compositematerial having a much larger specific surface area can be obtained.

(Other Modifications)

In the present invention, an exfoliated graphite-resin compositematerial is obtained by pyrolyzing a polymer in a composition having astructure in which a polymer in which a radical polymerizable monomer ispolymerized is grafted on graphite or primary exfoliated graphite, asdescribed above. In the present invention, further, the step ofexfoliating graphite may be performed by another method. For example,another method for exfoliating graphite as conventionally known may befurther carried out using an exfoliated graphite-resin compositematerial as a raw material as described above. Alternatively, the methodfor producing an exfoliated graphite-resin composite material accordingto the present invention may be carried out using as a raw materialprimary exfoliated graphite obtained by another method for exfoliatinggraphite. Also in these cases, an exfoliated graphite-resin compositematerial having a much larger specific surface area can be obtained. Assuch another method for exfoliating graphite, for example, a method forexfoliating graphite by electrochemical treatment, or anadsorption-pyrolysis method can be used.

The present invention will be clarified below by giving specificExamples and Comparative Examples. The present invention is not limitedto the following Examples.

Example 1

10 g of expanded graphite (manufactured by TOYO TANSO CO., LTD., tradename “PF Powder 8”), 20 g of ADCA having the structure represented bythe above formula (1) (manufactured by EIWA CHEMICAL IND. CO., LTD,trade name “AC#R-K3,” pyrolysis temperature 210° C.) as a pyrolyzablefoaming agent, and 200 g of a styrene monomer (manufactured by Wako PureChemical Industries, Ltd.) as a radical polymerizable monomer were mixedto provide a mixture. Next, the above mixture was subjected toultrasonic treatment at 100 W and an oscillation frequency of 28 kHz for120 minutes using an ultrasonic treatment apparatus (manufactured byHonda Electronics Co., Ltd.). Thus, a composition in which the aboveexpanded graphite was dispersed in the above styrene monomer wasobtained.

Next, the above composition was heated to a temperature of 120° C.,maintained for 1 hour, and further maintained at a temperature of 150°C. for 1 hour. Thus, the styrene monomer in the above composition waspolymerized.

Next, the above composition was further heated to a temperature of 230°C. and maintained at the temperature of 230° C. for 1 hour. Thus, theabove ADCA was pyrolyzed and foamed in the above composition.

Then, the above composition was further heated to a temperature of 430°C. and maintained at the temperature of 430° C. for 2 hours. Thus, thepolymer in which the styrene monomer was polymerized in the abovecomposition was pyrolyzed to obtain an exfoliated graphite-resincomposite material in which the above graphite was exfoliated.

Example 2

1000 mg of expanded graphite (manufactured by TOYO TANSO CO., LTD.,trade name “PF Powder 8,” BET specific surface area=22 m²/g), 2 g ofADCA having the structure represented by the above formula (1)(manufactured by EIWA CHEMICAL IND. CO., LTD, trade name “AC#R-K3,”pyrolysis temperature 210° C.) as a pyrolyzable foaming agent, 10 g of avinyl acetate polymer (SN-04T, manufactured by DENKA) as a radicalpolymerizable monomer, and 20 g of tetrahydrofuran were mixed to providea mixture. Next, the above mixture was subjected to ultrasonic treatmentat 100 W and an oscillation frequency of 28 kHz for 120 minutes using anultrasonic treatment apparatus (manufactured by Honda Electronics Co.,Ltd.). Thus, a composition in which the above expanded graphite wasdispersed in the above vinyl acetate polymer was obtained.

Next, the above composition was subjected to drying treatment at 80° C.for 2 hours and further heated to a temperature of 110° C. to completelydry the THF solution. The above composition was further maintained at atemperature of 230° C. for 2 hours. Thus, the above ADCA was pyrolyzedand foamed in the above composition.

Then, the above composition was further heated to a temperature of 500°C. and maintained for 2 hours. Thus, the vinyl acetate polymer in theabove composition was pyrolyzed to obtain an exfoliated graphite-resincomposite material in which the above graphite was exfoliated.

Example 3

6 g of expanded graphite (manufactured by TOYO TANSO CO., LTD., tradename “PF Powder 8,” BET specific surface area=22 m²/g), 12 g of ADCAhaving the structure represented by the above formula (1) (manufacturedby EIWA CHEMICAL IND. CO., LTD, trade name “AC#R-K3,” pyrolysistemperature 210° C.) as a pyrolyzable foaming agent, 120 g ofpolypropylene glycol PPG, manufactured by Sanyo Chemical Industries,Ltd., product number: SANNIX GP-3000, number average molecularweight=3000), and 120 g of tetrahydrofuran as a solvent were mixed toprovide a raw material composition. Next, the raw material compositionwas irradiated with ultrasonic waves at 100 W and an oscillationfrequency of 28 kHz for 2 hours using an ultrasonic treatment apparatus(manufactured by Honda Electronics Co., Ltd.). The polypropylene glycolwas adsorbed on the expanded graphite by this ultrasonic treatment. Inthis manner, a composition in which the polypropylene glycol wasadsorbed on the expanded graphite was provided.

After the above ultrasonic irradiation, the above composition was moldedby a solution casting method, maintained at a drying temperature of 80°C. for 2 hours, then maintained at a temperature of 110° C. for 1 hour,further maintained at a temperature of 150° C. for 1 hour, and furthermaintained at a temperature of 230° C. for 2 hours. Thus, the above ADCAwas pyrolyzed and foamed in the above composition.

Next, the heating step of maintaining the above composition at atemperature of 450° C. for 1.5 hours was carried out. Thus, the abovepolypropylene glycol was pyrolyzed to obtain an exfoliatedgraphite-resin composite material.

Reference Example 1

A composition in which expanded graphite was dispersed in a styrenemonomer was obtained as in Example 1.

Next, the above composition was heated as in Example 1 to pyrolyze andfoam the ADCA in the composition.

Then, the above composition was maintained at a temperature of 450° C.for 2 hours unlike Example 1. Thus, the polymer in which the styrenemonomer was polymerized in the composition was pyrolyzed to obtain anexfoliated graphite-resin composite material in which the graphite wasexfoliated.

Reference Example 2

A composition in which expanded graphite was dispersed in a vinylacetate polymer was obtained as in Example 2. Next, the ADCA waspyrolyzed and foamed in the composition as in Example 2.

Thereafter, the above composition was heated to a temperature of 500° C.and further maintained for 24 hours. Thus, the vinyl acetate polymer inthe above composition was pyrolyzed to obtain an exfoliatedgraphite-resin composite material in which the above graphite wasexfoliated.

Reference Example 3

A composition in which polypropylene glycol was adsorbed on expandedgraphite was provided as in Example 3.

As in Example 3, after ultrasonic irradiation, the composition wasmolded by a solution casting method and further heated to pyrolyze andfoam the ADCA in the composition.

Thereafter, the heating step of maintaining the composition at atemperature of 400° C. for 24 hours was carried out in Reference Example3. Thus, the polypropylene glycol was pyrolyzed to obtain exfoliatedgraphite.

[Evaluation of Examples and Reference Examples]

1) TG/DTA Measurement

a) A combustion test was performed in which the polymers polymerized orused in Examples 1 to 3 were heated from 30° C. to 1000° C. at a rate of10° C./min under an air atmosphere. The TG/DTA measurement results underthis combustion test are shown in FIGS. 1 to 3.

b) A combustion test was performed in which the exfoliatedgraphite-resin composite materials obtained by Examples 1 to 3 andReference Examples 1 to 3 were heated from 30° C. to 1000° C. at a rateof 10° C./min under an air atmosphere. The TG/DTA measurement resultsunder this combustion test are shown in FIGS. 4 to 6 and FIGS. 13 to 15.

From the comparison of FIGS. 1 to 3 with FIGS. 4 to 6, it is found thatthe pyrolysis initiation temperatures and pyrolysis end temperatures ofthe resins in the exfoliated graphite-resin composite materials arehigher than the pyrolysis initiation temperatures and pyrolysis endtemperatures of the resins before composite formation, respectively.

In addition, around 570° C. in all TG curves in FIGS. 4 to 6, inflectionpoints in the above TG curves are seen. Therefore, it is considered thatthe polymers are left at temperatures lower than the above inflectionpoints.

Further, the decomposition end point temperature of the originalexpanded graphite in all DTA curves in FIGS. 4 to 6 decreases, and thus,it is considered that exfoliation proceeds as a whole.

In addition, as is clear from FIG. 13 to FIG. 15, it is found that inReference Examples 1 to 3, the polymers are completely pyrolyzed and arenot left.

2) Measurement of BET Specific Surface Area

For the exfoliated graphite-resin composite materials obtained byExamples 1 to 3 and Reference Examples 1 to 3, the BET specific surfacearea was measured by a specific surface area measuring apparatusASAP-2000 manufactured by SHIMADZU CORPORATION using a nitrogen gas. Theresults are shown in the following Table 1.

TABLE 1 BET specific surface area (m²/g) Ex. 1 59 Ex. 2 119 Ex. 3 137Reference Ex. 1 37 Reference Ex. 2 28 Reference Ex. 3 37

As is clear from Table 1, it is found that compared with ReferenceExamples 1 to 3 in which the resin is not left, in Examples 1 to 3, theBET specific surface area can be increased because part of the resin isleft. In other words, it is found that the graphite exfoliation effectis increased by decomposition such that part of the resin is left.

3) XRD Measurement

The XRD spectra of the exfoliated graphite-resin composite materialsobtained by Examples 1 to 3 are shown in FIGS. 7 to 9.

As is clear from FIGS. 7 to 9, it is found that the crystallization peakintensity of the graphite structure of the original expanded graphitedecreases by performing exfoliation treatment.

4) Observation by SEM

The exfoliated graphite-resin composite materials obtained by Examples 1to 3 were magnified 1000 times and photographed by a scanning electronmicroscope (SEM), and the thus obtained photographs were observed. Theabove SEM photographs of the exfoliated graphite-resin compositematerials obtained by Examples 1 to 3 are shown in FIGS. 10 to 12.

As is also clear from FIGS. 10 to 12, it is found that exfoliatedgraphite-resin composite materials that were thin and had a largespecific surface area were obtained by the production methods of theExamples according to the present invention.

Examples 4 to 8

The exfoliated graphite-resin composite material of Example 4 wasobtained as in Example 3 with the blending ratio between the componentsbeing same and that of Example 3 but except that the total amount wasdecreased by 20% by weight.

In each of Example 5 to Example 8, the same treatment steps as Example 4were carried out to obtain an exfoliated graphite-resin compositematerial as in Example 4. In other words, Examples 5 to 8 correspond toexamples in which Example 4 is repeated. However, by increasing thetotal amount by 20% by weight, actually, the way of being fired variedpartially in the firing furnace though the firing temperature and thefiring time were the same. In other words, for operational reasons, thefiring temperature varied in the range of ±10° C.

Examples 9 to 12

The exfoliated graphite-resin composite material of Example 9 wasobtained as in Example 2 with the blending ratio between the componentsbeing same and that of Example 2 but except that the total amount wasincreased three times by weight.

In addition, in Examples 10 to 12, the same treatment steps as Example 9were carried out to obtain the exfoliated graphite-resin compositematerials of Examples 10 to 12. In other words, Examples 10 to 12correspond to examples in which Example 9 is repeated. However, byincreasing the total amount by 20% by weight, actually, the way of beingfired varied partially in the firing furnace though the firingtemperature and the firing time were the same. In other words, foroperational reasons, the firing temperature varied in the range of ±10°C.

Examples 13 to 14

In each of Example 13 to Example 14, each step treatment was carried outas in Example 4 except that the firing temperature and firing time inthe final step were changed to 400° C. and 10 hours.

For the exfoliated graphite-resin composite materials of Examples 4 to8, Examples 9 to 12, and Examples 13 and 14, the amount of methyleneblue adsorbed was measured by the following procedure.

Measurement of Amount of Methylene Blue Adsorbed Methanol solutions ofmethylene blue at concentrations of 10 mg/L, 5.0 mg/L, 2.5 mg/L, and1.25 mg/L were prepared in volumetric flasks. As the methylene blue,methylene blue that was a special grade reagent manufactured by KANTOCHEMICAL CO., INC. was used. Using an ultraviolet-visiblespectrophotometer (product number UV-1600) manufactured by SHIMADZUCORPORATION, the absorbance of the above four types of methylene bluesolutions provided was measured, and a calibration curve was prepared.

Next, 0.005 g of the methylene blue was placed in a 50 mL volumetricflask, and methanol was added as a measurement solvent to prepare a 100mg/L methylene blue solution. This methylene blue solution was diluted10 times using the measurement solvent to obtain a 10 mg/L methyleneblue solution.

A stir bar, a carbon sample to be measured (0.05 to 0.005 g, changedaccording to the BET value of the sample), and 50 mL of the above 10mg/L methylene blue solution were added to a 100 mL eggplant flask, andthen, the mixture was subjected to ultrasonic treatment for 15 minutesusing an ultrasonic cleaning machine. After the carbon sample wasdispersed in this manner, the dispersion was stirred in a cooling bathat a temperature of 25° C. for 60 minutes.

After adsorption equilibrium was reached, the carbon sample and thesupernatant liquid were separated by centrifugation. The absorbance ofthe 10 mg/L methylene blue solution that was blank and the absorbance ofthe above supernatant liquid were measured using the aboveultraviolet-visible spectrophotometer.

The difference between the absorbance of the above blank methylene bluesolution and the absorbance of the above supernatant liquid, that is,the amount of decrease in absorbance, was calculated. From this amountof decrease in absorbance and the slope of the above-describedcalibration curve, the amount of decrease in the concentration of themethylene blue solution was obtained. From this amount of decrease inthe concentration of the methylene blue solution, the amount ofmethylene blue adsorbed on the carbon surface was obtained by thefollowing formula.

the amount adsorbed (mol/g)={the amount of decrease in the concentrationof the methylene blue solution (g/L)×the volume of the measurementsolvent (L)}/{the molecular weight of the methylene blue (g/mol)×themass of the charged carbon sample (g)}

In addition, the BET specific surface areas of the exfoliatedgraphite-resin composite materials obtained in the above Examples 4 to14 were obtained.

Further, the grafting ratios of the resins in the exfoliatedgraphite-resin composite materials obtained in Examples 4 to 14 wereobtained by the following method.

Measurement of Resin Grafting Ratio (%) on Exfoliated Graphite

1 To 10 g of a sample containing a high pressure heatingreaction-treated carbon material was dissolved in a 50-fold weight of agood solvent. The solution was subjected to dispersion treatment at 45kHz and an output of 100 W at normal temperature for 30 minutes using anultrasonic apparatus.

The obtained solution was filtered using PTFE-T300A090C manufactured byAdvantec having a pore diameter of 3 μm while suction was performedusing an aspirator. Further, the same amount of a solvent as the amountof the solution was added, the mixture was filtered again, and thepolymer unreacted with the graphene was washed and filtered.

The sample on the filter paper was dried in an oven to remove thecontained solvent. The amount of the resin left was obtained from TG/DTAmeasurement results using the sample, and taken as the grafting ratio.

The amount of methylene blue adsorbed obtained as described above, theBET specific surface area, and the resin grafting ratio obtained fromthe BET specific surface area are shown in the following Table 2.

TABLE 2 BET specific Grafting Amount adsorbed surface area (m²/g) ratio(%) (μmol/g) Ex. 4 75 13 44.1 Ex. 5 87 13 43.9 Ex. 6 101 11 53.0 Ex. 7111 17 46.1 Ex. 8 130 23 71.1 Ex. 9 103 62 55.9 Ex. 10 107 62 47.2 Ex.11 115 64 45.1 Ex. 12 109 58 71.1 Ex. 13 49 2 15.4 Ex. 14 64 7 18.1Reference Ex. 4 25.4 0 6.2 Reference Ex. 5 113 0 14.7 Reference Ex. 6800 0 103.4 Reference Ex. 7 1270 0 170.9

In addition, the relationship between the above BET specific surfacearea and the amount of methylene blue adsorbed is shown in FIG. 16.

In FIG. 16 and FIG. 17, apart from the above Examples 4 to 14, therelationship between the BET specific surface area and the amount ofmethylene blue adsorbed measured as described above for knowncarbonaceous materials is shown together. In FIG. 16 and FIG. 17, thepoint P1 (Reference Example 4) shows the result of spherical graphite(manufactured by The Association of Powder Process Industry andEngineering, JAPAN, product number: RPSA-2). The point P2 (ReferenceExample 5) shows the result of spherical graphite (manufactured by TheAssociation of Powder Process Industry and Engineering, JAPAN, productnumber: RPSA-3). The point P3 (Reference Example 6) shows the result ofspherical graphite (Lion Corporation, product number: EC-300J, averageparticle diameter 40 nm). The point P4 (Reference Example 7) shows theresult of spherical graphite (Lion Corporation, product number:EC-600JD, average particle diameter 34 nm). In FIG. 16, only the abovefour points (Reference Examples 4 to 7) are plotted as known graphitematerials, but it has been confirmed that also in other knowncarbonaceous materials, the results are plotted near y=0.13x whereinr²=0.99 shown in FIG. 16 and FIG. 17.

On the other hand, it is found that in the exfoliated graphite-resincomposite materials of Examples 4 to 14, the amount of methylene blueadsorbed is considerably larger than y=0.13x as shown in FIG. 16 andFIG. 17. In other words, y>0.13x and y/x is 0.15 or more. When therelationship between y and x in Examples 4 to 14 shown in FIG. 16 andFIG. 17 was obtained, the result y=0.47x wherein r²=0.86 was obtained.

In other words, it is found that in the exfoliated graphite-resincomposite materials of the above Examples 4 to 14, the amount ofmethylene blue adsorbed that is wet-measured is very larger than the BETspecific surface area that is dry-measured. Therefore, it is found thatwhen each of the exfoliated graphite-resin composite materials of theabove Examples 4 to 14 is added to a resin in a state of a dispersion inwhich the exfoliated graphite-resin composite material is dispersed inmethanol, the dispersibility in the resin can be increased much more.

1. An exfoliated graphite-resin composite material comprising anexfoliated graphite and a resin said exfoliated graphite and said resinforming the exfoliated graphite-resin composite, and when an amount ofmethylene blue adsorbed per g of the exfoliated graphite-resin compositematerial (μmol/g) is y, the amount of methylene blue adsorbed asmeasured based on a difference between an absorbance of a methanolsolution of methylene blue at a concentration of 10 mg/L and anabsorbance of a supernatant liquid obtained by introducing theexfoliated graphite-resin composite material into the methanol solutionof methylene blue and performing centrifugation, and a BET specificsurface area (m²/g) of the exfoliated graphite-resin composite materialis x, a ratio y/x being 0.15 or more, and the BET specific surface areabeing 25 m²/g or more, and said exfoliated graphite-resin composite hasa graphite structure in the central portion and has an exfoliatedstructure in the edge portion.
 2. (canceled)
 3. The exfoliatedgraphite-resin composite material according to claim 1, wherein acontent of the resin is 1% by mass to 70% by mass.
 4. The exfoliatedgraphite-resin composite material according to claim 1, wherein theresin is a polymer of a radical polymerizable monomer. 5-18. (canceled)19. The exfoliated graphite-resin composite material according to claim1, wherein the ratio y/x is 0.27 or more.
 20. The exfoliatedgraphite-resin composite material according to claim 1, wherein theratio y/x is 0.39 or more.